The invention relates to a method and a device for determining the torque exerted on a body of revolution capable of being driven rotatably about an axis of rotation, in particular on the bottom bracket bearing shaft of a bicycle, with a first and a second measurement generator which are arranged on the body of revolution at an axial distance or a radial distance from one another and which consist of rings radially surrounding the body of revolution and composed of fields having an alternately different signal behavior, the number of fields of the two rings being identical, with a first measurement transducer assigned to the first measurement generator and with a second measurement transducer assigned to the second measurement generator, said measurement transducers both supplying output signals, from which first and second square-wave signals are formed, the average torque being determined from the distances between edges of the first and second square-wave signals over one complete revolution of the body of revolution.
A method and a device of the type initially mentioned are known from DE 40 38 413 A1. Here, one of the rings with the fields having an alternately different signal behavior is interrupted by a reference mark. This means that a measurement cycle can commence only whenever the reference mark moves past the measurement transducer assigned to it. This may mean, in an extreme situation, that an almost complete revolution of the body of revolution must first take place before a measurement cycle can commence. Furthermore, only one support point in any torque profile within one complete revolution is detected by means of this method. The calculation of the average torque or work during one or more complete revolutions can therefore be carried out correctly only when the torque is constant.
Furthermore, it is difficult to detect very small angles of rotation and low torques on the body of revolution, since limits are set by the manufacturing tolerances of, in particular, the rings surrounding the body of revolution and having the fields.
The object of the invention is, therefore, to provide a method and a device of the type initially mentioned, by means of which, along with the simple design, a measurement cycle is started, essentially without delay, after the commencement of an application of torque and it becomes possible to detect the actual average torque and the work performed.
This object is achieved, according to the invention, in that the fields having an alternately different signal behavior form uninterrupted rings, in that, over one or more complete revolutions of the nonloaded torque-free body of revolution, the edge distances Tml between specific edges of the first square-wave signals and the distances xcex1ml of specific edges of the second square-wave signals from specific edges of the first square-wave signals are in each case summed up and the torque-free ratio
xcex2ml=(xcex1ml1+xcex1ml2+ . . . xcex1min)/ (Tml2+Tml2+ . . . Tmin)+xcexa3xcex1min/xcexa3Tmin
is formed, in that, over one or more complete revolutions of the body of revolution loaded with the torque to be determined, the edge distances Tm between specific edges of the first square-wave signals and the distances am of specific edges of the second square-wave signals from specific edges of the first square-wave signals are in each case summed up and the applied-torque ratio
xcex2m=(xcex1m1+xcex1m2+ . . . xcex1mn)/ (Tm1+Tm2+ . . . Tmn)=xcexa3xcex1mn/xcexa3Tmn
is formed, in that the work on the applied-torque body of revolution is determined from the equation
xe2x80x83W=∫02xcfx80Mdxcfx86={overscore (M)}xc2x72xcfx80≈(xcex2mxe2x88x92xcex2ml)xc2x7k,
k being a calibration constant and xcfx86 being the angle of rotation of the body of revolution, and in that the average torque exerted on the body of revolution is determined from the equation
{overscore (M)}=W/2xcfx80≈(xcex2mxe2x88x92xcex2ml)xc2x7k/2xcfx80.
The distances Tml, Tml, xcex1ml and xcex1m as well as the time t may, at the same time, be detected by means of a high-accuracy counter having a high oscillator frequency. The torque-free ratio xcex2ml produces a reference value which already contains tolerance-induced deviations in the fields having a different signal behavior and the distances xcex1ml. This makes it possible, on the one hand, to produce the fields cost-effectively and at low outlay, since there are no high tolerances which have to be adhered to. On the other hand, the rings radially surrounding the body of revolution may be arranged on the latter, with their fields being assigned to one another in any way desired, thus making production considerably simpler and cheaper, and requiring no adjustment work. Since a measurement cycle always extends over one or more complete revolutions of the body of revolution, there is not only compensation of the tolerance-induced deviations of the fields, but a measurement cycle can also commence at any specific edge of the first square-wave signals, which means that, if there is a corresponding number of fields, the first measurement cycle already starts almost immediately after the commencement of the introduction of torque. There is no need to wait until a reference mark triggers a signal.
Furthermore, due to tolerance compensation, it is also possible to determine very low torques with high accuracy.
Over and above the average torque, the average power can also be formed according to the equation
{overscore (P)}=W/t=(xcex2mxe2x88x92xcex2ml)xc2x7k/t,
t being the time of one or more complete revolutions of the body of revolution.
So that variations in the application of torque to the body of revolution can be indicated in a simple way, one or more further measurement cycles may be carried out automatically after a measurement cycle has elapsed.
Since the calibration constant and the torque-free ratio xcex2ml are invariable quantities, in order to reduce the computer capacity, the calibration constant k and/or the torque-free ratio xcex2ml may be determined in a separate procedure and stored retrievably as constant storage values for each torque determination.
In order to form the torque-free ratio xcex2ml or the applied-torque ratio xcex2m, the edge distances between the adjacent equally directed or the adjacent oppositely directed edges of the first square-wave signals may be summed up.
In the same way, in order to form the torque-free ratio xcex2ml or the applied-torque ratio xcex2m, the distances of specific edges of the first square-wave signals from the adjacent equally directed or adjacent oppositely directed edges of the second square-wave signals may be summed up.
If very high torques are applied to the body of revolution, the torsion of the latter may lead to a distance xcex1m extending beyond the end of the distance Tm assigned to it into the next following distance Tml. This would result in false determination of the torque. In order to avoid such false torque determination, when the torque-free ratio xcex2ml is formed, the distances xcex1ml between specific edges of the second square-wave signals may be compared with a specific predetermined edge distance xcex1max and, if xcex1ml greater than xcex1max is detected, the measurement cycle may be discontinued and a new measurement cycle may be commenced, in which, instead of the distances xcex1ml, those distances xcex1mlxe2x80x2 are summed up, the start of which corresponds to the start of xcex1ml and the ends of which are those oppositely directed edges of the second square-wave signals which precede the ends of the distances xcex1ml.
In order to avoid further torque detection when the body of revolution is at a standstill or virtually at a standstill after torque has been detected, after the commencement of a measurement cycle for determining the torque the instantaneous rotational speed or angular speed of the body of revolution may be detected and compared with a specific limit value of the rotational speed or angular speed, and the measurement cycle may be discontinued if the said speed falls short of the limit value. As soon as the angular speed or the rotational speed exceeds the specific limit value again, a measurement cycle is started again immediately with the specific edge of the first square-wave signals which is next detected.
So that the detected torque profile can be comprehended by an observer, the specific torque may be indicated on an indicator.
Furthermore, for further communication of information, it is advantageous if, in addition to the torque, further quantities capable of being derived from the torque are indicated on the indicator.
In a simple embodiment of a device for carrying out the method, the signals detected by the first and second measurement transducers are fed to an electronic computer unit which has memories for storing the torque-free ratio xcex2ml and/or the calibration constant k and/or the specific limit value of the rotational speed or angular speed of the body of revolution and/or the specific edge distance xcex1max and by which an output signal corresponding to the torque to be determined can be generated.
So that the torque values determined are capable of being read off, an indicator unit may be capable of being activated by the output signal from the computer unit.
If the electronic computer unit is a microcontroller or microcomputer, this saves construction space.
In principle, the first and second measurement generators and measurement transducers may operate by the most diverse methods, such as, for example, optical, capacitive or inductive methods. It is also perfectly possible for the first measurement generators and measurement transducers to operate by a method other than that of the second measurement generators and measurement transducers. In an advantageous development, however, the first and/or the second measurement generators comprise fields having an optically different signal behavior and the first and/or the second measurement transducers are transducers detecting an optically different signal behavior.
In this case, depending on the construction space available, the first and/or the second measurement generators may consist of a measuring disk or a measuring cylinder which has the fields with a different signal behavior on its radial plane face or on its cylindrical outer face.
The fields may have a different reflex behavior, and this may be achieved, for example, in that the fields have alternately high and low reflection.
Another possibility is for the fields to be formed alternately by slits and diaphragm portions of the measuring disk.